util/qemu-coroutine.c

   1 /*
   2  * QEMU coroutines
   3  *
   4  * Copyright IBM, Corp. 2011
   5  *
   6  * Authors:
   7  *  Stefan Hajnoczi    <stefanha@linux.vnet.ibm.com>
   8  *  Kevin Wolf         <kwolf@redhat.com>
   9  *
  10  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  11  * See the COPYING.LIB file in the top-level directory.
  12  *
  13  */
  14
  15 #include "qemu/osdep.h"
  16 #include "trace.h"
  17 #include "qemu/thread.h"
  18 #include "qemu/atomic.h"
  19 #include "qemu/coroutine_int.h"
  20 #include "qemu/coroutine-tls.h"
  21 #include "qemu/cutils.h"
  22 #include "block/aio.h"
  23
  24 enum {
  25     COROUTINE_POOL_BATCH_MAX_SIZE = 128,
  26 };
  27
  28 /*
  29  * Coroutine creation and deletion is expensive so a pool of unused coroutines
  30  * is kept as a cache. When the pool has coroutines available, they are
  31  * recycled instead of creating new ones from scratch. Coroutines are added to
  32  * the pool upon termination.
  33  *
  34  * The pool is global but each thread maintains a small local pool to avoid
  35  * global pool contention. Threads fetch and return batches of coroutines from
  36  * the global pool to maintain their local pool. The local pool holds up to two
  37  * batches whereas the maximum size of the global pool is controlled by the
  38  * qemu_coroutine_inc_pool_size() API.
  39  *
  40  * .-----------------------------------.
  41  * | Batch 1 | Batch 2 | Batch 3 | ... | global_pool
  42  * `-----------------------------------'
  43  *
  44  * .-------------------.
  45  * | Batch 1 | Batch 2 | per-thread local_pool (maximum 2 batches)
  46  * `-------------------'
  47  */
  48 typedef struct CoroutinePoolBatch {
  49     /* Batches are kept in a list */
  50     QSLIST_ENTRY(CoroutinePoolBatch) next;
  51
  52     /* This batch holds up to @COROUTINE_POOL_BATCH_MAX_SIZE coroutines */
  53     QSLIST_HEAD(, Coroutine) list;
  54     unsigned int size;
  55 } CoroutinePoolBatch;
  56
  57 typedef QSLIST_HEAD(, CoroutinePoolBatch) CoroutinePool;
  58
  59 /* Host operating system limit on number of pooled coroutines */
  60 static unsigned int global_pool_hard_max_size;
  61
  62 static QemuMutex global_pool_lock; /* protects the following variables */
  63 static CoroutinePool global_pool = QSLIST_HEAD_INITIALIZER(global_pool);
  64 static unsigned int global_pool_size;
  65 static unsigned int global_pool_max_size = COROUTINE_POOL_BATCH_MAX_SIZE;
  66
  67 QEMU_DEFINE_STATIC_CO_TLS(CoroutinePool, local_pool);
  68 QEMU_DEFINE_STATIC_CO_TLS(Notifier, local_pool_cleanup_notifier);
  69
  70 static CoroutinePoolBatch *coroutine_pool_batch_new(void)
  71 {
  72     CoroutinePoolBatch *batch = g_new(CoroutinePoolBatch, 1);
  73
  74     QSLIST_INIT(&batch->list);
  75     batch->size = 0;
  76     return batch;
  77 }
  78
  79 static void coroutine_pool_batch_delete(CoroutinePoolBatch *batch)
  80 {
  81     Coroutine *co;
  82     Coroutine *tmp;
  83
  84     QSLIST_FOREACH_SAFE(co, &batch->list, pool_next, tmp) {
  85         QSLIST_REMOVE_HEAD(&batch->list, pool_next);
  86         qemu_coroutine_delete(co);
  87     }
  88     g_free(batch);
  89 }
  90
  91 static void local_pool_cleanup(Notifier *n, void *value)
  92 {
  93     CoroutinePool *local_pool = get_ptr_local_pool();
  94     CoroutinePoolBatch *batch;
  95     CoroutinePoolBatch *tmp;
  96
  97     QSLIST_FOREACH_SAFE(batch, local_pool, next, tmp) {
  98         QSLIST_REMOVE_HEAD(local_pool, next);
  99         coroutine_pool_batch_delete(batch);
 100     }
 101 }
 102
 103 /* Ensure the atexit notifier is registered */
 104 static void local_pool_cleanup_init_once(void)
 105 {
 106     Notifier *notifier = get_ptr_local_pool_cleanup_notifier();
 107     if (!notifier->notify) {
 108         notifier->notify = local_pool_cleanup;
 109         qemu_thread_atexit_add(notifier);
 110     }
 111 }
 112
 113 /* Helper to get the next unused coroutine from the local pool */
 114 static Coroutine *coroutine_pool_get_local(void)
 115 {
 116     CoroutinePool *local_pool = get_ptr_local_pool();
 117     CoroutinePoolBatch *batch = QSLIST_FIRST(local_pool);
 118     Coroutine *co;
 119
 120     if (unlikely(!batch)) {
 121         return NULL;
 122     }
 123
 124     co = QSLIST_FIRST(&batch->list);
 125     QSLIST_REMOVE_HEAD(&batch->list, pool_next);
 126     batch->size--;
 127
 128     if (batch->size == 0) {
 129         QSLIST_REMOVE_HEAD(local_pool, next);
 130         coroutine_pool_batch_delete(batch);
 131     }
 132     return co;
 133 }
 134
 135 /* Get the next batch from the global pool */
 136 static void coroutine_pool_refill_local(void)
 137 {
 138     CoroutinePool *local_pool = get_ptr_local_pool();
 139     CoroutinePoolBatch *batch = NULL;
 140
 141     WITH_QEMU_LOCK_GUARD(&global_pool_lock) {
 142         batch = QSLIST_FIRST(&global_pool);
 143
 144         if (batch) {
 145             QSLIST_REMOVE_HEAD(&global_pool, next);
 146             global_pool_size -= batch->size;
 147         }
 148     }
 149
 150     if (batch) {
 151         QSLIST_INSERT_HEAD(local_pool, batch, next);
 152         local_pool_cleanup_init_once();
 153     }
 154 }
 155
 156 /* Add a batch of coroutines to the global pool */
 157 static void coroutine_pool_put_global(CoroutinePoolBatch *batch)
 158 {
 159     WITH_QEMU_LOCK_GUARD(&global_pool_lock) {
 160         unsigned int max = MIN(global_pool_max_size,
 161                                global_pool_hard_max_size);
 162
 163         if (global_pool_size < max) {
 164             QSLIST_INSERT_HEAD(&global_pool, batch, next);
 165
 166             /* Overshooting the max pool size is allowed */
 167             global_pool_size += batch->size;
 168             return;
 169         }
 170     }
 171
 172     /* The global pool was full, so throw away this batch */
 173     coroutine_pool_batch_delete(batch);
 174 }
 175
 176 /* Get the next unused coroutine from the pool or return NULL */
 177 static Coroutine *coroutine_pool_get(void)
 178 {
 179     Coroutine *co;
 180
 181     co = coroutine_pool_get_local();
 182     if (!co) {
 183         coroutine_pool_refill_local();
 184         co = coroutine_pool_get_local();
 185     }
 186     return co;
 187 }
 188
 189 static void coroutine_pool_put(Coroutine *co)
 190 {
 191     CoroutinePool *local_pool = get_ptr_local_pool();
 192     CoroutinePoolBatch *batch = QSLIST_FIRST(local_pool);
 193
 194     if (unlikely(!batch)) {
 195         batch = coroutine_pool_batch_new();
 196         QSLIST_INSERT_HEAD(local_pool, batch, next);
 197         local_pool_cleanup_init_once();
 198     }
 199
 200     if (unlikely(batch->size >= COROUTINE_POOL_BATCH_MAX_SIZE)) {
 201         CoroutinePoolBatch *next = QSLIST_NEXT(batch, next);
 202
 203         /* Is the local pool full? */
 204         if (next) {
 205             QSLIST_REMOVE_HEAD(local_pool, next);
 206             coroutine_pool_put_global(batch);
 207         }
 208
 209         batch = coroutine_pool_batch_new();
 210         QSLIST_INSERT_HEAD(local_pool, batch, next);
 211     }
 212
 213     QSLIST_INSERT_HEAD(&batch->list, co, pool_next);
 214     batch->size++;
 215 }
 216
 217 Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque)
 218 {
 219     Coroutine *co = NULL;
 220
 221     if (IS_ENABLED(CONFIG_COROUTINE_POOL)) {
 222         co = coroutine_pool_get();
 223     }
 224
 225     if (!co) {
 226         co = qemu_coroutine_new();
 227     }
 228
 229     co->entry = entry;
 230     co->entry_arg = opaque;
 231     QSIMPLEQ_INIT(&co->co_queue_wakeup);
 232     return co;
 233 }
 234
 235 static void coroutine_delete(Coroutine *co)
 236 {
 237     co->caller = NULL;
 238
 239     if (IS_ENABLED(CONFIG_COROUTINE_POOL)) {
 240         coroutine_pool_put(co);
 241     } else {
 242         qemu_coroutine_delete(co);
 243     }
 244 }
 245
 246 void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co)
 247 {
 248     QSIMPLEQ_HEAD(, Coroutine) pending = QSIMPLEQ_HEAD_INITIALIZER(pending);
 249     Coroutine *from = qemu_coroutine_self();
 250
 251     QSIMPLEQ_INSERT_TAIL(&pending, co, co_queue_next);
 252
 253     /* Run co and any queued coroutines */
 254     while (!QSIMPLEQ_EMPTY(&pending)) {
 255         Coroutine *to = QSIMPLEQ_FIRST(&pending);
 256         CoroutineAction ret;
 257
 258         /*
 259          * Read to before to->scheduled; pairs with qatomic_cmpxchg in
 260          * qemu_co_sleep(), aio_co_schedule() etc.
 261          */
 262         smp_read_barrier_depends();
 263
 264         const char *scheduled = qatomic_read(&to->scheduled);
 265
 266         QSIMPLEQ_REMOVE_HEAD(&pending, co_queue_next);
 267
 268         trace_qemu_aio_coroutine_enter(ctx, from, to, to->entry_arg);
 269
 270         /* if the Coroutine has already been scheduled, entering it again will
 271          * cause us to enter it twice, potentially even after the coroutine has
 272          * been deleted */
 273         if (scheduled) {
 274             fprintf(stderr,
 275                     "%s: Co-routine was already scheduled in '%s'\n",
 276                     __func__, scheduled);
 277             abort();
 278         }
 279
 280         if (to->caller) {
 281             fprintf(stderr, "Co-routine re-entered recursively\n");
 282             abort();
 283         }
 284
 285         to->caller = from;
 286         to->ctx = ctx;
 287
 288         /* Store to->ctx before anything that stores to.  Matches
 289          * barrier in aio_co_wake and qemu_co_mutex_wake.
 290          */
 291         smp_wmb();
 292
 293         ret = qemu_coroutine_switch(from, to, COROUTINE_ENTER);
 294
 295         /* Queued coroutines are run depth-first; previously pending coroutines
 296          * run after those queued more recently.
 297          */
 298         QSIMPLEQ_PREPEND(&pending, &to->co_queue_wakeup);
 299
 300         switch (ret) {
 301         case COROUTINE_YIELD:
 302             break;
 303         case COROUTINE_TERMINATE:
 304             assert(!to->locks_held);
 305             trace_qemu_coroutine_terminate(to);
 306             coroutine_delete(to);
 307             break;
 308         default:
 309             abort();
 310         }
 311     }
 312 }
 313
 314 void qemu_coroutine_enter(Coroutine *co)
 315 {
 316     qemu_aio_coroutine_enter(qemu_get_current_aio_context(), co);
 317 }
 318
 319 void qemu_coroutine_enter_if_inactive(Coroutine *co)
 320 {
 321     if (!qemu_coroutine_entered(co)) {
 322         qemu_coroutine_enter(co);
 323     }
 324 }
 325
 326 void coroutine_fn qemu_coroutine_yield(void)
 327 {
 328     Coroutine *self = qemu_coroutine_self();
 329     Coroutine *to = self->caller;
 330
 331     trace_qemu_coroutine_yield(self, to);
 332
 333     if (!to) {
 334         fprintf(stderr, "Co-routine is yielding to no one\n");
 335         abort();
 336     }
 337
 338     self->caller = NULL;
 339     qemu_coroutine_switch(self, to, COROUTINE_YIELD);
 340 }
 341
 342 bool qemu_coroutine_entered(Coroutine *co)
 343 {
 344     return co->caller;
 345 }
 346
 347 AioContext *qemu_coroutine_get_aio_context(Coroutine *co)
 348 {
 349     return co->ctx;
 350 }
 351
 352 void qemu_coroutine_inc_pool_size(unsigned int additional_pool_size)
 353 {
 354     QEMU_LOCK_GUARD(&global_pool_lock);
 355     global_pool_max_size += additional_pool_size;
 356 }
 357
 358 void qemu_coroutine_dec_pool_size(unsigned int removing_pool_size)
 359 {
 360     QEMU_LOCK_GUARD(&global_pool_lock);
 361     global_pool_max_size -= removing_pool_size;
 362 }
 363
 364 static unsigned int get_global_pool_hard_max_size(void)
 365 {
 366 #ifdef __linux__
 367     g_autofree char *contents = NULL;
 368     int max_map_count;
 369
 370     /*
 371      * Linux processes can have up to max_map_count virtual memory areas
 372      * (VMAs). mmap(2), mprotect(2), etc fail with ENOMEM beyond this limit. We
 373      * must limit the coroutine pool to a safe size to avoid running out of
 374      * VMAs.
 375      */
 376     if (g_file_get_contents("/proc/sys/vm/max_map_count", &contents, NULL,
 377                             NULL) &&
 378         qemu_strtoi(contents, NULL, 10, &max_map_count) == 0) {
 379         /*
 380          * This is an upper bound that avoids exceeding max_map_count. Leave a
 381          * fixed amount for non-coroutine users like library dependencies,
 382          * vhost-user, etc. Each coroutine takes up 2 VMAs so halve the
 383          * remaining amount.
 384          */
 385         if (max_map_count > 5000) {
 386             return (max_map_count - 5000) / 2;
 387         } else {
 388             /* Disable the global pool but threads still have local pools */
 389             return 0;
 390         }
 391     }
 392 #endif
 393
 394     return UINT_MAX;
 395 }
 396
 397 static void __attribute__((constructor)) qemu_coroutine_init(void)
 398 {
 399     qemu_mutex_init(&global_pool_lock);
 400     global_pool_hard_max_size = get_global_pool_hard_max_size();
 401 }